DESCRIPTION: This proposal is from an established investigator who has published excellent work in this field. He seeks to continue to characterize the interactions between the mesoderm and the extracellular matrix as it forms in early Xenopus embryos. As mesoderm cells form in the embryo, they become motile, and by a complex and ill-understood mechanism, move inside the embryo. As they do so, they behave differently according to whether they will form dorsal, ventral, anterior or posterior structures. One of the substrata of the ingressing mesoderm is the extracellular matrix secreted by the cells of the blastocoel roof. It is the interaction between mesoderm cells and the extracellular matrix glycoprotein that is the subject of this proposal. The aims are 1) to establish the roles of cell-matrix interactions during gastrulation using function-blocking reagents, 2) To develop "reporters" of sites of integrin activation that will be used to monitor stage and region-specific changes in receptor activation, and 3) to see if patterns of mesodermal gene expression require cell-ecm interaction.